In vivo swelling kinetics of a series of hydrogel polymers in the cannulated gastrointestinal tract of the canine

Hydrogels for oral controlled drug delivery must swell as they move through the various regions of the gastrointestinal tract. Residence time in these different regions, coupled with available water and local environmental conditions, can potentially influence the rate and extent of swelling. The objective of this study is to regio-specifically study the in vivo swelling behavior of hydroxypropyl methyl cellulose, carboxylmethyl cellulose sodium salt, Carbopol 974P(TM), and Noveon AA1(TM) (polycarbophil) in the duodenal and ileal regions of the small intestine of cannulated canines in fasted and fed states, atropine sulfate permitted the study of the influence of secretions on swelling. For each of the hydrogels studied, swelling was observed to be greater in the duodenum than the ileum with in vivo swelling not being strongly influenced by the fed condition or by the presence or absence of secretions. We propose that the fluid necessary for polymer swelling is primarily derived from the aqueous mucous gel coating the epithelial cells lining the small intestine. Differences in swelling rate and extent in ileal and duodenal regions may be due to differences in the amount and thickness of mucous in the two regions.